1. Field of the Invention
The present invention relates to a transfer device for transferring a substrate such as a glass substrate for a liquid crystal display, and more particularly to a transfer device for transferring a substrate to be used in a reduced-pressure chamber.
2. Description of the Related Art
There are known treatments such as etching and ashing for a glass substrate for an LCD (hereinafter called simply an LCD substrate) in a process chamber which are performed under reduced pressure. The reduced-pressure chamber system includes a load lock chamber to preliminarily generate vacuum atmosphere. The load lock chamber allows an interior chamber to avoid normal room pressures every time an LCD substrate is loaded/unloaded to the process chamber.
In such a load lock chamber, an LCD substrate transferring device is provided and the transferring device transfers the LCD substrate between the respective chambers (load lock chamber and interior chamber, for example).
FIG. 1 shows a conventional transferring device 3 to be used in transferring the LCD substrate. The transferring device 3 comprises arms 4, 5 and a stage 6. A LCD substrate 2 is mounted on the stage 6. Rubber projections 7 are formed on an upper surface 6a of the stage 6. These projections 7 are used so as to prevent the LCD substrate 2 from slipping off the stage 6 during the transferring operation.
In recent years, in accordance with increase in demand for LCDs, it has been desired to improve the LCD manufacturing device, which can manufacture a large amount of LCDs in a short period time, that is, improvement of the through put of an LCD manufacturing device.
In order to improve the through put of an LCD manufacturing device, not only treating time of the treating device to be used in each treatment process but also time for transferring the LCD substrate 2 by use of these treatment devices is required.
However, according to the conventional transferring device 3, the LCD substrate 2 is moved on the stage 6, and shifted from the position where the substrate 2 should be placed as the transferring speed is increased. In other words, if acceleration or deceleration is increased, an inertia force to be applied to the LCD substrate 2 is increased, so that the LCD substrate 2 is shifted from the home position (or reference position) on the stage 6. The term "home position" used in the above means a predetermined reference position, which is determined in every treatment section in order to treat the LCD substrate 2 in a post-process, for example, center position of each treatment section.
If the actual position of the LCD substrate 2 is shifted from the home position, the treatment in the post-process cannot be speedily and correctly carried out. For example, if the LCD substrate 2 is not placed at the predetermined position in the process chamber, a desirable treatment cannot carried out. Moreover, if the LCD substrate 2 collides with an inlet/outlet gate of the chamber the LCD substrate 2 may be broken.
Furthermore, the LCD substrate transferring device must be contained in a narrow space of the load lock chamber. A conventional transferring device, as disclosed in Published Unexamined Japanese Patent Application No. 1-198465, comprises at least a driving motor for expanding and retracting a link arm and a driving motor for rotating the link arm.
However, in such a transferring device, there are needed two or more driving motors, a microcomputer for controlling these motors and a sensor, and the device is enlarged and complicated.
In particular, in the transferring device provided in the load lock chamber, a magnetic sealing mechanism must be provided in the driving shafts of these driving motors. However, the cost of such a magnetic sealing mechanism is high, and if the sealing positions are increased, the cost of the device is increased.
Moreover, since the number of structural parts is large in the conventional transferring device, the trouble rate of the device is high, and reliability is low. In a case where the load chamber is adjacent to the etching chamber, dust or particles generated by the rotation shaft of the multi-shaft driving are adhered to the LCD substrate, and the so-call contamination of products is generated.
Furthermore, in the substrate transferring device provided in the load lock chamber for realizing high vacuum, the width of the space, which is necessary for the rotations of the link arm and the substrate, must be narrowed as much as possible such that the transferring operation is realized in the narrow space and the load lock chamber is miniaturized.